The invention relates to carburation devices for internal combustion engines of the kind comprising an auxiliary throttle means in their induction pipe, upstream of a main throttle means actuated by the driver, the auxiliary throttle means automatically and progressively opening in proportion to the increase in the flow rate of air travelling through the pipe and actuating a metering device regulating the flow rate of fuel coming from a fuel source at substantially atmospheric pressue and flowing into the pipe due the the underpressure between the two throttle means, the air flow section metered by the auxiliary throttle means being substantially proportional to the fuel flow section metered by the metering means, and the air and fuel, which are thus introduced under the same pressure difference, from a mixture having a substantially constant richness during normal operation of the engine.
It is known that the standards for atmospheric pollution very strictly limit the richness of the air-fuel mixtures in carburetors, in order to reduce the proportion of polluting gases in the exhaust gases. To this end, it is already known to provide a carburation device having a servo-motor which permanently adjusts the cross-section of the orifices supplying the fuel and/or air of the mixture, the servo-motor being actuated in accordance with the characteristics of the exhaust gases in an attempt to control the richness of the mixture automatically. A system using a servo-motor for metering the orifices is however quite expensive.
It is an object of the invention to provide a carburation device, wherein the richness of the air-fuel mixture is automatically adjusted and which uses simple, rugged and relatively inexpensive means for that purpose.
To this end, there is provided a carburation device having means for adjusting the richness of the mixture in response to the characteristics of the engine exhaust gases, said means comprising a solenoid valve which is actuated periodically and for an overall period of time which is adjusted in dependence on said characteristics thereby alternately opening and closing means delivering air to a fuel circuit connecting the fuel source to the induction pipe.
The invention will be more clearly understood from the following description and accompanying drawings, both of which relate to particular embodiments, given by way of examples.